<p>In this study, we aimed to investigate the effects of cumulative doses of Zn²⁺ (by exposing samples to 1&#xa0;µM, 10&#xa0;µM, and 100&#xa0;µM ZnCl₂) on myocardial papillary muscle contractions isolated from rat hearts in vitro and the roles of the zinc finger protein ZEB1 in this effect. In these preparations, 100&#xa0;µM ZnCl₂ application in different protocols caused a decrease in contraction force and an increase in contraction time in both frequency-dependent parameters and pre-expected stimuli when compared to the control group. Our study data show that Ca²⁺ homeostasis is closely related to increasing Zn²⁺ doses (especially at 100&#xa0;µM ZnCl₂ dose). Secondly, the levels of ZEB1, a zinc finger protein, were also significantly lower in the 100&#xa0;µM ZnCl₂ group compared to the other groups, which seems to be related to the increase in Ca²⁺ that triggers ROS production at high doses of Zn²⁺. The data of our study, which we conducted to understand the Zn²⁺ concentrations in the heart and to reveal new mechanisms that play a role in the regulation of Ca²⁺ dynamics in heart tissue and is the first research in the literature on this subject, show that in vitro zinc application may have a dose-dependent effect on myocardial papillary muscle contractions.</p>